John Stacey Adams (1963)
This theory of motivation highlights the effects of environment and respect. To assess this particularly subjective feeling, the individual compares his or her situation with another person in a similar position, inside or outside the company.
Here, we're dealing more with elements of satisfaction than with elements of motivation. However, as Herzberg showed, not achieving a good level of satisfaction negatively impacts motivation.

More and more theories are integrating the subjective aspect of motivation, making them more realistic and complex to measure.